This invention is generally directed to foundational units used in the construction of furniture and is specifically directed to a drop-in spring assembly unit utilizing grid inserts to interlock spring elements.
Spring assemblies used in the manufacture of furniture are often made of a plurality of springs arranged in rows or columns and jointly attached to a grid structure which overlaps the springs. U.S. Pat. No. 4,426,070 demonstrates such as assembly. In this particular device, the spring assembly comprises a base frame, a grid frame and coil springs connected at the base and within the grid frame. Here, the grid frame is a single structure extending over the spring elements. The grid structure is specifically designed to hold the spring elements in place without an external coupling means. Regardless, the manufacture of the grid structure is work intensive requiring the welding of many intersections. In addition, the construction of the unit is further complicated by the need to identify and fit each spring element to its proper location on the grid structure of the assembly unit.
Other conventional methods of assembly for units having grid structures include cross helical hook up, hook and lace wire hook up and hand tie. However, none of the prior art methods offer a grid structure which will not overlay the springs, nor do any of the methods provide a cushion clip means for connecting rows of spring elements that simplifies the construction of the unit and maximizes the resiliency of the springs.
In a typical assembly unit, the grid structure is composed of a one piece grid comprising a series of interlaced wires which are welded at their intersections and joined to the spring elements and a border wire by welding or wrapping. The one piece grid is typically designed to prevent longitudinal sagging. However, because it is one piece, it does not allow coils to interact with each other to maximize spring resiliency and offer a firmer, stronger unit. The resiliency of assembly units is provided by the springs which in the prior art units are oriented either beneath the intersections of the grid wires or between adjacent grid wires, depleting their full effectiveness.
There exists a need, therefore, for a simplified drop-in spring assembly unit that results in a stronger foundation at the same or less cost.